textproduct: Rapid City

KEY MESSAGES

- Upper ridge will dominate the weather through early next week.

- Isolated severe thunderstorms may occur late Saturday afternoon and evening, especially across northeast Wyoming.

- Temperatures will average about 4-8F above normal.

UPDATE

Issued at 1053 PM MDT Fri Aug 21 2026

A couple stray showers or thunderstorms are possible overnight across the south-central South Dakota plains, sticking fairly close to the Nebraska border, with dry conditions elsewhere. Next round of thunderstorm potential still on track for late Saturday afternoon and evening across northeast Wyoming, spreading eastward into South Dakota with time later Saturday evening. A severe cell or two with damaging winds and large hail will be possible, especially west of the Black Hills, as forecast soundings and HREF guidance support 1,000 to 2,000 J/kg of SBCAPE combined with sufficient moisture and deep-layer shear as high as 40kts. Instability may tend to wane a bit east of the Black Hills, where some early-evening capping in forecast soundings also casts some uncertainty on thunderstorm evolution. Currently do carry PoPs eastward across our South Dakota zones from late evening into the overnight as everything trends east.

DISCUSSION

(This Afternoon Through Thursday) Issued at 1149 AM MDT Fri Aug 21 2026

Current upper-air analysis and water vapor imagery depict large- scale ridging continuing to strengthen over the southwest. Satellite imagery indicates partly cloudy skies behind the thunderstorms and showers that moved through the region this morning. Current radar scans show a few weak returns associated with showers/virga over western SD. Surface observations show temperatures mainly in the 80s, with dewpoints in the 40s across northeast WY transitioning to the low 60s across south-central SD. Winds are generally easterly across western SD and southerly across northeast WY at 10 to 17kts, gusting to 25kts. Campbell Co. in particular may see gusty northeasterly winds up to 25kts, behind a weak frontal passage, and minRH values in the upper teens this afternoon. Due to these conditions, elevated fire weather concerns will continue to persist through this afternoon for Campbell Co.

There is still uncertainty around today's chances for thunderstorms across southwestern SD, both in timing and severity, with disagreement remaining among the CAMs. However, MLCAPE values of ~750-1250 J/kg, dewpoints in the 50s to low 60s in the SD plains, and 0-6km bulk wind shear values around 55kts indicate that the environment in southwestern SD could support thunderstorm development and a supercell or two. The timing of the shortwave today, the cap currently in place, and the strong vertical moisture gradient between the SD plains and the Black Hills will all play a large role in storm development this afternoon/evening and into the overnight hours.

Due to these factors, there is a slight risk for severe thunderstorms southeast of Rapid City down to the SD/NE border, with the primary threats being large hail (up to 2") and damaging winds (60-70+ mph). As a result, 15 percent POPs were added to the southern Black Hills and into southwestern SD for this afternoon into the evening.

Multiple disturbances riding along the ridge will keep scattered thunderstorms chances in play for Saturday and Sunday, with northeast WY favored for better coverage Saturday. As is typical for thunderstorms in August, chances for precipitation will be hit-and- miss. Cloud cover and storm placement will also drive day-to-day temperatures, though highs are expected to remain above average across most of the region through the weekend and into next week as the ridge remains in place.

AVIATION

(For the 06Z TAFS Through 06Z Saturday Night) Issued At 1040 PM MDT Fri Aug 21 2026

VFR conditions are expected through the forecast period. Breezy conditions are expected across the area Saturday afternoon, with +20kt gusts expected. Far northeast WY may see some showers tomorrow evening, but confidence is still relatively low. Still, the PROB30 for KGCC was retained at 22Z.

FIRE WEATHER

Issued At 1149 AM MDT Fri Aug 21 2026

Elevated fire weather concerns will continue through this afternoon for Campbell Co., where gusty northeasterly winds up to 25kts will combine with minimum relative humidity values in the upper teens. Thunderstorm chances increase across northeast Wyoming late Saturday afternoon, increasing the dry lightning risk, however, relative humidity values will increase to the upper 30s to low 40s.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.